This invention relates to an apparatus and method for drying objects with fluids.
Drying critical parts and objects is a crucial and important part of the overall manufacturing process in many fields and industries including, but not limited to, semiconductor, optical, metal, electronic packaging and assembly, medical, and others. In many cases, drying parts after a cleaning process is very important, if not essential. For different reasons, the reliability and future performance of the objects are closely related to the effectiveness and quality of the drying cycle. Different drying methods are utilized. Most common are the use of thermal energy and gas flow, vapor drying, rotational spinning, water dissolution, capillary dry, water dispersion, and Marangoni flow effects.
A brief discussion of these prior art drying methods is necessary in order to more fully understand the shortcomings of the prior art solutions to drying objects.
1. Thermal drying. These methods are relatively effective but have clear limitations in that they are time-consuming, they consume considerable amounts of energy, and, most critically, they create "spotting" on the surfaces due to water evaporation leaving behind dissolved salts and particles.
2. Vapor drying. This method utilizes a solvent capable of forming a water azetrope which is heated into a vapor phase and then is directed to contact the objects to be dried for the removal of water residues. This method is highly effective although it is limited by safety/hazard concerns since the solvents that are used are generally flammable. Further, it also consumes considerable energy.
3. Rotational spinning. This method spins the object to be dried and then typically includes a stage whereby a heated gas is directed on the object. Although this method minimizes "spotting" by removing the water droplets by means of centrifugal forces prior to evaporation, it too has clear limitations. Only certain types of flat objects can be arranged in a spinning apparatus. Moreover, the objects maintain physical contact with the holders or attachments, thus introducing a source for physical deterioration and particle contamination.
4. Marangoni flow effect. This method consists of spraying a small amount of alcohol vapor on a water surface under which the objects are immersed. The objects to be dried are then slowly lifted. At the water surface, the alcohol lowers the water surface tension, enhancing "wetability" consequently. The alcohol droplets form an upper layer that forces the water to be removed from the surface of the objects as they are lifted from the water bath. This methodology has been widely accepted, in the semi-conductor industry in particular. However, this technology is generally used in conjunction with a thermal drying method where a hot nitrogen flow is directed toward the surface of the object in order to aid in the drying of the residual alcohol/water film left on the surface of the object. As with thermal drying, spotting is a problem as well as the fact that forced gas movement inside the drying chamber has the potential of inducing particle re-deposition by the flow of residual particles.
5. Capillary dry. This method is very similar to the Marangoni flow method described above. In this method, objects are immersed in a hot water bath. They are then slowly pulled upwards out of the hot water bath. At the water/air interface, the capillary forces of the water tend to pull most of the water residue off of the object. Generally, a thin water layer is left behind on the surface. Since hot water is used, this layer will tend to evaporate very rapidly, particularly if a hot gas flow is applied to the surface of the object as well. As with the previous Marangoni method, particle re-deposition and spotting may occur.
6. Water displacement. This method involves the use of a highly volatile halogenated solvent aided by a surfactant. The objects to be dried are immersed in the solvent where the surfactant attaches to the surfaces of the objects, replacing the water as a result. The objects are then lifted from the liquid and placed in a solvent vapor zone where condensation takes place and the surfactant is removed by the solvent. This method is not considered highly reliable because it is difficult to determine whether all the surfactant has been removed from the objects' surfaces.
7. Water dissolution. This method is very similar to the water displacement process. In this case, however, the highly volatile solvent relies on a small amount of 2-Propanol which is used to dissolve water residues. The main limitation of this method is that the solvent/alcohol blend becomes "loaded" with water relatively fast, which essentially renders the solvent spent and useless.
These methods and procedures are exemplified by way of example, to the best of the Applicant's knowledge in the following United States patents: Matthews, U.S. Pat. No. 5,727,578; Britten, U.S. Pat. No. 5,660,642; Bran, U.S. Pat. No. 5,556,479; Ferrell, U.S. Pat. No. 5,653,045; Mohindra, et al., U.S. Pat. Nos. 5,571,337 and 5,634,978; Giles, et al., U.S. Pat. No. 4,924,890; Kusukara, U.S. Pat. No. 4,736,758; and McConnell, et al., U.S. Pat. Nos. 4,984,597 and 4,911,761. Each of these suffers from the disadvantages set forth above including but not limited to the use of solvents that do not completely dry items, thereby requiring additional processing steps such as the use of ultraviolet drying procedures, as well as the need for the interaction of mechanical devices to move the materials to be dried, among others.
Again, all of the prior art of which the inventor is aware suffers from one or more of the above-described limitations. Thus, there is a need in the art for providing an apparatus and method for drying objects which does not involve the use of thermal energy, does not use extremely flammable solvents, is not limited exclusively to thin, flat objects, does not require sophisticated and expensive equipment, upon which the drying effectiveness is not dependent upon the number of cycles or frequency of usage, and, most importantly, an apparatus and method by which the drying cycle time is faster and which prevents particle re-deposition and spotting on an object's surface. It, therefore, is an object of this invention to provide and improved object drying apparatus and method using fluids to dry objects quickly and without spotting and re-deposition of particles.